The present invention relates to the field of flame retardants (FRs) and, more particularly, to novel flame retardant compositions that are highly beneficial for use in textiles.
Textiles are an essential part of everyday life and are found, for example, in draperies, cloths, furniture and vehicle upholsteries, toys, packaging material and many more applications. Consequently, textile flammability is a serious industrial concern.
The flammability of fabrics is typically determined by the nature of the fiber comprising the fabric. Thus for example, some synthetic fibers, such as melamine, polyaramides, carbonized acrylic, and glass, are inherently flame resistant, whereby others, such as cotton, polyester and linen, can readily ignite. For those, the degree of flammability varies according to the fiber type and characteristics. For example, a textile made of a blend of fibers usually burns faster and to higher temperatures compared with each fiber type alone. Fabric flammability also depends on the fabric thickness and/or looseness.
The term “fiber” as defined hereinafter refers to a natural or synthetic filament capable of being spun into a yarn or made into a fabric.
The terms “fabric”, “textile” and “textile fabric” are used herein interchangeably to describe a sheet structure made from fibers.
Several approaches have been proposed heretofore for minimizing the fire hazard of flammable textiles:
One approach involves fiber copolymerization: several fiber monomers are mixed and copolymerized, thus improving the properties of a certain fiber (e.g., a flammable fiber) through the enhanced properties of another fiber (e.g., a fire resistant fiber). However, this technique is limited by the number of existing fibers and their properties, and cannot be tailor-made for any substrate or requirements. Furthermore, fiber types and fiber polymerization types are not necessarily compatible, thus further limiting the applicability of this technique. An additional disadvantage of this approach is the high cost of the fire resistant fibers.
Another approach involves the introduction of flame retardants (FR) in or on the fabric, using one of two methodologies:
(i) Chemical post treatment: the fabric is treated with flame retardant chemicals after it has been produced, either by coating the fabric, or by the introduction of the FR into the fabric during the final dyeing process. The flame retardant can be applied to the back of the fabric (termed “back-coating”) or to its front (termed “front-coating”), depending on the specific fabric application. For example, for draperies, furniture upholstering garments and linen, where the aesthetic appearance of the front side of the fabric is most important, back-coating is desired.
A disadvantage of this methodology is the common need to apply the protective coating in large amounts (commonly termed “high add-on”) in order to obtain the required flame-resistant characteristics. Often, such high add-on adversely affects otherwise desirable aesthetical and textural properties of the fabric. Thus, for example, upon application of a FR, fabrics may become stiff and harsh and may have duller shades and poor tear strength and abrasion properties.
(ii) Fiber-additive matrix (also termed “compounding”): the FR is linked to the fiber during the melt spinning process, such that a fiber-additive molten plastic matrix is formed. This methodology has many drawbacks: (i) degradation of the FR agent due to the high extrusion temperatures, (ii) reaction of the FR agent with the extruded fiber, and subsequent modification of the fiber properties, such as fiber dyeability, fiber processability or other physical properties of the fiber, and (iii) reaction of the FR agent with the various polymeric additives, such as dyes or catalysts.
Another classification of FRs is according to the type of bonding between the FR and the fiber: a flame retardant is termed “additive” when it is mixed into, but not chemically reacted or bound to the fiber material. “Additive” FRs often easily migrate into the environment. A flame retardant is termed “reactive” when it is chemically inserted into the structure of the fiber material. “Reactive” FRs are bound to the fabric and hence do not easily migrate from the product into the environment and furthermore, typically do not degrade the physical properties of the fiber.
Another serious problem in designing flame retardant fabrics, is fabric smoldering, which is particularly critical in fabrics that contain a high ratio of cellulose (such as, for example cotton, viscose, linen or other vegetable fibers).
Thus, while some textiles may be resistant to open flame burning, the smoldering (also termed “after flame”), which may persist after the open flame has been extinguished, can eventually lead to complete digestion of the fabric (see, for example, “Toxicological Risks of Selected Flame-Retardant Chemicals-2000”, Donald E. Gardner (Chair), Subcommittee on Flame-Retardant Chemicals, Committee on Toxicology, Board on Environmental Studies and Toxicology, National Research Council). Obviously, this leads to failure in many standard flammability tests (see, for example, U.S. Pat. Nos. 3,955,032 and 4,600,606; and V. Mischutin, “Nontoxic Flame Retardant for Textiles” in J. Coated Fabrics, Vol. 7, 1978, pp. 308-318).
Although one solution to this problem is coating the textile fabric with an impermeable material, obviously the feel of such a product is greatly damaged.
Accordingly, in order to overcome the smoldering problem in textiles, the addition of a smoldering suppressant (SS), which is also referred to herein, interchangeably, as a smoldering suppressing agent, is frequently required, in addition to the flame retardant agent.
Selecting the suitable flame retardant and/or smoldering suppressant, and the suitable methodology for applying it to the fabric largely depends on the substrate which has to be protected: the protection of a garment, or the protection of an electrical appliance will inherently pose different requirements and restrictions of the flame retardant used.
When used in textiles, an applied flame retardant has to be: (a) compatible with the fabric, (b) non-damaging to the aesthetical and textural properties of the fabric, (c) transparent, (d) light stable, (e) resistant to extensive washing and cleaning, (f) environmentally and physiologically safe, (g) of low toxic gas emittance, and (h) inexpensive. Above all, a flame retardant should pass the standard flammability tests in the field.
Properties of the FR such as stability to UV light, heat, water, detergents and air-pollutants, as well as chemical stability, may be summed-up under the term “durability”. The most durable textiles are those which are inherently flame retardant, or which contain reactive (chemically bound) FRs. In the latter, the degree of durability depends on the strength of the bonds between the flame retardant formulation and the fiber. Additive (mixed) FRs, or chemically applied FRs which are water-soluble, are considered less durable. Furthermore, topically applied FR agents are generally not as durable as those which are incorporated into the fabric during the extrusion of the fiber. Thus, the topically applied FR agent may be washed off during the laundry cycle, and in these cases the expensive and burdensome dry cleaning of the textile has to be used. Currently, there are no clear-cut standards to define fabric durability, and it is commonly defined as a fabric meeting its performance standard after 5, 10 or 50 washes.
Presently, there are four main families of flame-retardant chemicals:                Inorganic flame retardants (such as aluminum oxide, magnesium hydroxide and ammonium polyphosphate);        Halogenated flame retardants, primarily based on bromine and chlorine;        Organophosphorus flame retardants, which are primarily phosphate esters; and        Nitrogen-based organic flame retardants.        
Bromine-containing compounds have been long established as flame retardants. For example, U.S. Pat. Nos. 3,955,032 and 4,600,606; and Mischutin [“Nontoxic Flame Retardant for Textiles” in J. Coated Fabrics, Vol. 7, 1978, pp. 308-318] teach flame retardation of textiles using formulations containing aromatic bromine compounds which are adhered to the substrates by means of binders.
The use of aromatic bromines as FRs for textiles, however, suffers major disadvantages including, for example, high bromine content demand, high dry add-on and/or binder demand, and a need to add compounds which enhance the flame retardancy (hereinafter termed a synergist). In addition, application of such FRs on fabrics may result in streak marks on dark fabrics, excessive dripping during combustion of thermoplastic fibers, relatively high level of smoldering and a general instability of the flame retardant dispersion which may prevent a uniform application thereof on the fabric. Most of these drawbacks are inherent to the aromatic bromine compounds currently in use [see, for example, “Toxicological Risks of Selected Flame-Retardant Chemicals-2000”, Donald E. Gardner (Chair) Subcommittee on Flame-Retardant Chemicals, Committee on Toxicology, Board on Environmental Studies and Toxicology, National Research Council].
Using existing bromine-containing FR formulations, a dry add-on of 60% or higher (compared to the dry fabric weight) is often required to obtain satisfactory flame retardation. This high add-on is due in part to the large amount of binder needed to affix the FR agents to the textile. The binder used in bromine-containing formulations typically constitutes about 50% by weight of the total FR formulation [Toxicological Risks of Selected Flame-Retardant Chemicals, page 506-507, V. Mischutin, Nontoxic Flame Retardant for Textiles, J. Coated Fabrics, Vol. 7, 1978, p. 315] and due to its substantial presence, contributes in itself to flammability and dripping, thus requiring even higher loading of bromine and creating an inefficient cycle. Furthermore, brominated FR formulations often suffer from storage instability.
Ongoing research has therefore been conducted in order to obtain flame-retardants with improved performance, which are less detrimental to textile properties. Research has been particularly focused on providing an efficient FR which requires low binder content and is characterized by good dispersion properties.
Recently, it has been shown that formulations combining phosphates and halogens display a synergism in flame retardation [E. S. Lee, “Possible Phosphorous Synergy in Polyester-Cotton Fabric Treated with Tetrabromobisphenol A and Diammonium Phosphate” in J. App. Pol. Sci., Vol. 84, 2002, pp. 172-177]. It has further been shown that phosphate and borate compounds are efficient solid phase flame retardants during combustion (G. Camino, M. P. Luda, “Fire Retardancy of Polymers: The use of Intumescents”, M. Le Bras, G. Camino, S. Bourbigot, R. Delobel, The Royal Society of Chemistry, 1888, p. 48, R. Dombrowski, Formulating Flame Retardant Coatings, Coated Fabrics Technology, Clemson University, 1998).
Compositions which combine compounds containing aromatic bromine atoms and compounds containing aliphatic bromine atoms are characterized by a broader temperature range for flame retardation, since the different bromine atoms react at different temperatures. This broader range creates more efficient flame retardation and hence, lower add-on of these compounds is required. An example of such flame retardant compositions is described in WO 05/103361, which is incorporated by reference as if fully set forth herein, and includes a combination of tris(tribromophenyl)triazine and tetrabromobisphenyl A-bis(2,3-dibromopropyl ether).
Combining the two bromine types within a single compound, has additional obvious advantages, such as reduced handling, enhanced compatibility, and less dispersion and application complexities.
Pentabromobenzylbromide (PBBBr) is an exemplary compound containing both an aromatic bromine and a benzylic bromine.
WO 06/008738 teaches a process for the preparation of highly pure PBBBr and its use as a co-flame retardant in the preparation of FR expanded polystyrene foams (EPS). WO 06/013554 teaches a styrenic polymer composition comprising a flame retardant, such as PBBBr and analogs thereof. These patent applications, however, fail to teach the use of PBBBr as a flame retardant for application on textiles, in which, as stated above, binders are often required so as to achieve the desirable results.
Japanese Patent No. 47032298 teaches the use of PBBBr as a flame retardant that is incorporated to the fabric by melt spinning with polyester fibers.
In all of these examples, PBBBr was used as a flame retardant or as a co-flame retardant incorporated within the polymer in the melt. As detailed above, it is preferred to apply the flame retardant topically on the fabric, thereby avoiding the thermal degradation of the FR agent during melting, as well as preventing the adverse effect of the FR agent on the processability and on other properties of the fiber. However, as is further detailed above, it is difficult to topically apply an FR agent to textiles since topically applied FRs are easily washed off during the laundry cycle.
It is therefore not surprising that PBBBr has never been prepared as a part of a coating or finishing formulation, and has been only known to be directly incorporated into the polymeric fiber, where it was used either alone or in combination with other flame retardants.
There is thus a widely recognized need for, and it would be highly advantageous to have, novel flame retardant formulations devoid of the above limitations.